Germicidally active soap containing silver salt of aromatic sulfinic acid



GERMICHDALLY ACTIVE SOAP CONTAINING SKLVER SALT F ARQMATIC SULFINIC ACID Garson A. lLutz, Columbus, and Robert E. Sharpe, Worthington, Uhio, assiguors, by mesne assignments, to Perrnachem Corporation, Palm Beach, Fla., a corporation of Florida N 0 Drawing. Application February 20, 1956 Serial No. 566,371

4- Claims. (Cl. 252-107) This invention relates to germicidally active soaps and more particularly to soaps containing a germicidally active silver salt.

Germicidal agents for use in soaps must possess a combination of properties which very few substances possess. In the first place, the germicide must be one which kills microorganisms on contact of very short duration. Another requirement for germicides for use in soaps is that they must not be harmful to human skin. Furthermore, the soap must not interfere with the germicidal action of the compound. A number of compounds which are effective germicides in other applications are ineffective as germicides in soap. Very few compounds have been found heretofore to have any n'oticeable effectiveness as germicides in soap, and none have been found to possess a high degree of effectiveness.

Various silver compounds have long been known to be effective bactericides in various applications. Silver salts in general have been most effective in applications where the salt remained in contact with the material to be sterilized for a substantial period of time. Because a compound to be effective as a germicide in soap must kill organisms on very brief contact time, it is not surprising that silver salts have been generally regarded as not being good germicides in soap.

According to the present invention it has been found that soaps containing a silver salt of an aromatic sulfinic acid kill skin bacteria rapidly under ordinary washing conditions. The silver salt is incorporated in small amounts in a conventional soap. Silver salts of either aromatic monosulfinic acids or aromatic polysulfinic acids may be used as germicidal agents. Substituents may replace hydrogen atoms in the aromatic nucleus. The silver salts of sulfinic acids of aromatic hydrocarbons such as benzene and its homologues have been found to be effective germicides in soap. Silver benzenesulfinate, C H SO Ag,

, has been found to be outstandingly eifective in killing bacteria, and has also been found to inhibit the growth of fungi. Silver ortho-toluene sulfinate is also bacteriotoxic, although a less potent bactericide in soap than silver benzenesulfinate.

The germicidal activity of soaps containing silver salts of aromatic sulfinic acids-is unexpected in view of the fact that some other silver salts of sulfur-containing compounds, such as the silver salts of saccharin and mercaptobenzothiazole, have little or no germicidal activity in soaps. Furthermore, simple silver salts have not been found to be effective germicides prior to this invention.

The germicides according to the present invention kill a large number of different types of bacteria, even when incorporated in relatively small amounts in soap. These compounds, when incorporated in soaps at a concentration' of about 500 parts per million of silver are very rapid in their action against bacteria. The silver concentration in the soaps may be considerably lower than this, for example, as low as 100 parts per million of silver or even lower. Higher concentrations than 500 parts per million of silver may be incorporated in soap. In gengtgs A att eral, these higher concentrations are unnecessary, as the germicides are highly effective in concentrations of 500 parts per million in soap.

The silver salts which are used in soap germicides of the present invention may be incorporated in any of the conventional fatty acid soaps. These soaps may be in the form of bar soap for hand or bath use, soap powders, shaving cream, or liquid soap.

The major constituent of soaps according to the present invention is a conventional fatty acid soap, that is, an alkali metal soap of one or more of the fatty acids such as lauric acid, stearic acid, palmitic acid, or oleic acid. A mild soap having a pH of about 7 to 10 is particularly desirable as the soap base. Soaps containing a silver salt of an aromatic sulfinic acid according to this invention have substantially the same mildness as the soap base.

Conventional methods may be used to prepare the germicidally active ingredients according to the present invention. A convenient method of preparing these ingredients is to react an aqueous solution of a silver salt, such as silver nitrate, with a solution of the acid corresponding to silver salt desired. A number of the aromatic sulfinic acids are insoluble in water. Acids which are insoluble or slightly soluble in water may be dissolved in a watermiscible organic solvent, such as methanol or ethanol, in which the acid is sufliciently soluble. Alcohols, such as methanol or ethanol, are preferred solvents. The reagents in their respective solutions are then reacted to form the silver salt of the aromatic sulfinic acid. This silver salt constitutes the germicidally active ingredient in the soaps of this invention.

The silver compound may be incorporated in the soap by conventional methods, during crutching or milling, for example. Soap may be mixed with the silver compound to be incorporated and a limited amount of water, and the resulting mix agitated to form a paste. The soap in paste form then may be formed into a large piece or slab and cut into bars. Where a soap in paste form, such as a shaving cream, is desired, it is necessary only to mix the ingredients in the desired proportions.

The invention will nowbe described with reference to specific examples.

EXAMPLE I Silver benzenesulfinate was prepared by dissolving 8.2 grams of sodium benzenesulfinate in 400 milliliters of water and adding 8.0 grams of silver nitrate dissolved in about 20 milliliters of water. A bulky white precipitate was formed. This precipitate was filtered, and washed with water, and dried at 60 to 70 C.

One hundred grams of white granular soap and 230 milligrams of silver benzenesulfinate prepared as described above were dry mixed in a Waring Blendor. The mixture was blended until it started to dust. Then an additional grams of the White granular soap were added and blended thoroughly. Blending was continued for several minutes. This reduced the soap to very fine particle size and thoroughly blended the silver benzenesulfinate with the soap. The dry blend was then transferred to the bowl of a household mixer. Then 250 milliliters of water were added and the mixture was blended to a thick, smooth paste. The paste was transferred to a 10 x 14-inch glass plate and formed into a cake 6 x 10 inches with a stainless steel spatula. The large cake was scored with the spatula into 20 cakes, each 1 /2 x 2 inches and approximately /2 inch thick. After air drying for several hours at room temperature, the cakes were separated and turned over. Drying was completed at room temperature.

The bacteriotoxicity of the soap was tested in handwashing tests by five persons. The persons used as test subjects were chosen at random and had widely varying bacterial counts on their hands. Each person moistened his hands and forearms up to a distance 14 inches above the tip of the middle finger on each hand for 25 seconds in a wash basin containing 2 liters of water. Then each person worked up a lather on the hands with a bar of soap prepared as described above in this example. This lathering took 25 seconds, and was followed by an additional 75 seconds of scrubbing of the entire test area. Each person then rinsed the lather from the test area in the wash basin for 20 seconds. Each person repeated this washing test for a total of times in a separate wash basin each time before drying his hands. The persons used a control soap, prepared as described above except for the absence of any silver compound, for the first three washings. The remaining washings were with soap containing silver benzenesulfinate, prepared as described above.

To compare the effectiveness of soaps of the present invention with an ordinary mild soap containing no bactericidal additives, the identical washing test was on a group of 16 persons selected at random, using the control soap.

Samples were taken from each wash basin to determine the bacterial count. The average bacterial count after each of the ten washings was obtained for both the test soap containing silver benzenesulfinate and the control soap. The average microbe count after each of the ten washings, in number of microorganisms in 0.1 milliliter, and the percentage reduction in bacterial count in each washing compared to the preceding washing, are given in Table 1 below for the test soap containing silver benzenesulfinate and for the control soap.

Table I SOAP CONTAINING SILVER BENZENESULFINATE Microbe Percent Count Reduction Number of Washlngs (microbes from in 0.1 ml.) Previous Basin 1 Control soap used in first three washings.

The first two washings (numbers 4 and 5) with the test soap containing silver benzenesulfinate caused a reduction of more than twothirds in the microbe count. This is considerably greater than the reduction in any two consecutive washings with the control soap. Soaps according to the present invention kill skin bacteria at a rapid rate when the microbe count is high or moderate, as the above results indicate. 7

EXAMPLE II To prepare silver benzenesulfinate for testing as a germicidal agent in soap solutions, 8.2 grams of sodium benzenesulfinate were dissolved in 200 milliliters of water, and 8.0 grams of silver nitrate dissolved in 100 milli- 4 liters of water were added. A bulky white precipitate was formed, and 200 milliliters of water was added to thin out the slurry. The precipitate in aqueous slurry was filtered a total of three times. The filter cakes obtained in the first two filtrations were reslurried in water for refiltration. Portions of the third filter cake were used to make up and test aqueous soap solutions containing silver benzenesulfinate, as will be described in Examples IV and V below.

EXAMPLE III Silver ortho-toluenesulfinate was prepared by adding 8.0 grams of silver nitrate dissolved in about 20 to 25 milliliters of water to 8.9 grams of sodium ortho-toluencsulfinate in 400 milliliters of water. A bulky white precipate was formed. This precipitate was filtered three times, and the filter cakes from the first two filtrations were reslurried in Water for further filtration. The precipitate darkened somewhat during filtration and reslurrying. A portion of the filter cake from the third filtration was used to make up an aqueous soap solution containing silver ortho-toluenesulfinate as will be described in Example IV below.

EXAMPLE IV The bacteriotoxicities of aqueous soap solutions of the silver salts prepared as described in Examples II and III were determined according to the test procedure described below. About 0.5 to 1 gram of the salt was placed in a filter paper in a conical funnel and leached with 500 milliliters of water, which was introduced into the tunnel in portions of about milliliters each. Onehalf (0.5) gram of a white granular soap powder was added to the filtrate in each instance, and the solution was warmed slightly to facilitate dissolution of the soap. A control solution containing 0.5 gram of soap powder dissolved in 500 milliliters of water, with no silver salt present, was also prepared.

The silver content of each filtrate was detemiined prior to the addition of soap. One milliliter of the filtrate, 6 milliliters of zolon red indicator consisting of 0.20 gram per liter of zolon red and 1.0 gram per liter of anhydrous sodium carbonate, and 13 milliliters of water, were mixed. The optical density of the solution of each salt was meas ured with a 560-millimicron monochromatic light and compared with a series of standard solutions to determine the silver content. The standard solutions contained various predetermined amounts of silver and 3 milliliters of zolon red indicator each in 10 milliliters. Results are given in Table 2 below.

The bactericidal activity of the soap solution of each salt was tested as described below, using test cultures of Bacillus subtilis, Escherichia coli, and Micrococcus pyogenes var. aureus. Nutrient broth having the following composition was prepared:

This broth was boiled for 20 minutes, poured into 10- milliliter tubes and autoclaved for 15 minutes at 121 C. and 15 pounds per square inch steam pressure.

Test cultures of Bacillus subtilis, Escherichia coli, and M icrococcus pyogenes var. aureus were transferred from their respective stock culture media to IO-milliliter portions of the nutrient broth. The cultures were incubated in their respective broths for 24 hours at 37 C. Each culture was transferred through a total of three broths, all of identical composition and volume. Transfers were made at intervals of 24 hours, and in each case one milliliter of the culture was transferred to the next nutrient broth. After incubation for 3 days, one milliliter of each culture was mixed with a IO-milliliter portion of the soap 5 solution to be tested. The soap solutions were maintained at 30 C. throughout the tests.

Transfers of soap solutions incubated with the test organisms to sterile broth were made at 5-minute intervals. A 4-millimeter loop was used to make the transfer, and the volume of material transferred was approximately 0.01 milliliter. The first transfer was made immediately upon mixing of the test culture with the soap solution. Thereafter, additional transfers to separate sterile broths were made 5 and 10 minutes after mixing. The subcultures obtained by transferring incubated solution to sterile broth were incubated for 24 hours at 37 C. At the end of this time they were observed for evidence of bacterial growth.

Table 2 below shows the effectiveness of the soaps prepared according to this invention as bactericidal agents. For each soap, the greatest time of exposure of the test organisms to the soap which resulted in a positive subculture is indicated. An asterisk indicates that the organism was not killed even after 10 minutes of exposure to the soap. This indicates that the soap solution was nontoxic or substantially nontoxic to that organism. A low number in the following table thus indicates a high degree of toxicity. The numeral thus indicates that the organism is killed very rapidly, i. e., in less than minutes, upon exposure to the germicidal soap solution.

The results of bactericidal testing, and the silver contents of each silver salt solution, are given in Table 2 1 All subcultures obtained from this organism and solution were fertile. The test was discontinued after minutes of exposure of the organism to the solution.

EXAMPLE V A test solution of silver benzenesulfinate and soap was prepared as follows: about 0.5 to 1 gram of silver benzenesulfinate, prepared as described in Example II, was placed in a filter paper in a conical funnel and leached with 250 milliliters of water. Then 0.1 gram of a white granular soap powder was added to a IOO-milliliter portion of the filtrate.

An inoculum of a mixture of fungi commonly found in air samples consisting of Rhizopus nigricans, Aspergillus niger, Penicillium luzeum, and Alternarz'a oleracea, was prepared by scraping the growth of 7-day slants, and suspending the mycelia and spores in about 150 milliliters of water containing 250 parts per million of a wetting agent, Triton X100. Triton X- is the proprietary name of an alkyl aryl polyether alcohol, a nonionic wetting agent, sold by Rohm & Haas Co., Philadelphia, Pennsylvania. Triton X-100, the condensation product of diisobutyl phenol and ethylene oxide, has a molecular weight of about 600 and an estimated average of nine or ten ethylene oxide groups per molecule. The suspension was filtered through 2 layers of cheesecloth.

One milliliter of the inoculum was pipetted into a 10- milliliter sample of the test solution. The sample of test solution with suspended fungus was agitated by hand. After 15 to 30 minutes, one milliliter of the suspension was pipetted onto nutrient agar in Petri plates. The nutrient agar had the following composition:

Beef extract grams 5 Peptone do 5 Agar do 15 Water milliliters 1000 The subculture on the Petri plate was incubated at 30 C. and was observed to be sterile after 7 days of incubation. Control plates showed fungus growth after 48 hours.

While the present invention has been described with reference to specific embodiments thereof, it is understood that this description is by way of illustration and not limitation.

What is claimed is:

1. A germicidally active soap composition comprising a water-soluble higher fatty acid soap and a germicidal amount of a silver salt of a sulfinic acid selected from the group consisting of benzene sulfinic acid selected from substituted benzene sulfinic acid.

2. A germicidally active soap composition comprising a water-soluble, higher fatty acid soap and a germicidal amount of a silver salt of a methyl substituted benzene sulfinic acid.

3. A germicidally active soap composition comprising a water-soluble, higher fatty acid soap and a germicidal amount of silver benzenesulfinate.

4. A germicidally active soap composition comprising a water-soluble, higher fatty acid soap and a germicidal amount of silver ortho-toluenesulfinate.

Schulenburg Mar. 5, 1935 Kunz et al Dec. 26, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,864,769 December 16, 1958 Garson A. Lutz et a1.

It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 35, for "selected from" read and a methyl Signed and sealed this 21st day of April 1959.

(SEAL) Attest:

KARL H, AXLINE f ROBERT C. WATSON Attesting Oificer Commissioner of Patents 

1. A GERMICIDALLY ACTIVE SOAP COMPOSITION COMPRISING A WATER-SOLUBLE HIGHER FATTY ACID SOAP AND A GERMICIDAL AMOUNT OF A SILVER SALT OF A SULFINIC ACID SELECTED FROM THE GROUP CONSISTING OF BENZENE SULFINIC ACID SELECTED FROM SUBSTITUTED BENZENE SULFINIC ACID. 